Carburetor



Sept. 10, 1935. M p lss 2,013,734

CARBURETOR Filed Feb. 1, 1932 F Z INVENTOR;

4uyusf/n M prmf/Iss ATTORNEY.

Patented Sept. 10, 1935 CARBURETOR Augustin M. Prentiss, San Antonio, Tex. Application February 1, 1932, Serial No. 590,296 27 Claims. (01. 261-76) This invention pertains to carburetors and more particularly has reference to compensating carburetors of the pressure feed type.

This invention isan improvement on the invention set forth in my United States Patent No. 1,329,309 issued January 27, 1920.

- In the patent cited I pointed out the advantages of pressure feed of the liquid fuel over suction feed thereof and showed how, due to the difference between the laws of flow of liquids and gases, it was impossible to maintain parity between the air fiow and liquid fuel fiow through a carburetor where both are produced bya common vacuum. I then pointed out that a parity could be secured by properly varying either the pressure on the liquid fuel supply or the pressure on the air supply or both. In the patent cited I varied the pressure on the liquid fuel in order to secure compensation of the liquid fuel fiow and thus obtain the desired parity. In this case, in order to maintain the desired parity between the air supply and liquid fuel supply to the carburetor, I vary the, pressure on the supplementary air only. By supplementary air, in this specification, I mean that part of. the carburetor air supply which is introduced into the mixing chamber under a superatmospheric pressure through the fuel nozzle and which is employed to break up and atomize the liquid fuel jet. By the term predetermined ratio, used in this application, I mean such a controlled ratio between the fuel and air components of the mixture as will cause this ratio to vary with the speed and load of the engine in accordance .with any desired curve of variation which curve has been'previously determined as the best for optimum engine performance under all operating conditions. Thus, if a rich mixture is desired for idling and for high speed operation, and a leaner mixture for economy at intermediate speeds, these results are secured by applicant's invention with proper adjustment of the controls.

Unless specially controlled and regulated to the contrary, the flow of liquid fuel through a carburetor follows the general law of liquid flow and the flow of air follows the law of adiabatic gas flow. As to the air flow, it is logical to assume that the expansion of a gas approaching an orifice, being rapid, is adiabatic, and the authorities generally agree that the flow of air through a carburetor is, for all practical purposes, sensibly adiabatic. The observed data support this view. a

The general formula for liquid flow and adiabatic gas flow, as applied to a carburetor, may be expressed as follows:

G1 is the rate of liquid flow in pounds per second. 10 G2 is the rate of air flow in pounds per sec- U1 is the coeflicient of eillux for liquid flow.

U2 is the coefiicient of efliux for adiabatic gas flow. 15

F1 isthe cross-sectional area of the liquid fuel passageway of the carburetor-generally the area of the metering restriction in the fuel passageway.

F2 is the cross-sectional area of the main air 20 passageway of the carburetor in the zone of the fuel jet orifice-generally the area of the smallest section of the Venturl throat.

1 is the unit weight of the liquid fuel, in pounds per cubic foot at 32 F. temperature. 25 72 is the unit weight of the air in pounds per cubic footat normal atmospheric pressure and g is the acceleration of gravity.

, Pn 'is the superior pressure causing the fluid 30 fiow, which, in suction-operated carburetors, is the atmospheric pressure outside the carburetor.

Pm is the absolute pressure in the mixing chamber of the carburetor in the zone of the fuel Jet orifice. 35

The foregoing nomenclature and formulas are, in accordance with Church's Mechanics of Engineering Part IV, Chapter VIII on Kinetics of gaseous fluids.

For convenience of reference in this speclilca- 40 tion, ,I shall followChurchs terminology and refer to the formula for liquid flow (formula (1) above) as the water formula and the formula for air flow, (formula (2) above), as the adiabatic formula. It willalso be understood that where I refer, in this specification, to the air supply to the mixing chamber of the carburetor as being fed into said chamber in accordance with the law of liquid flow, I mean in accordance with the water formula (formula (1) above). That is to say, the weight of air passing into the mixing chamber, per unit of time, for'any given pressure (vacuum) in said chamber, is that found from the .water formula" ((1) above) for Pm equal to the pressure (vacuum) in said in accordance with the normal law of air flow, I

mean in accordance with the adiabatic gas formula (formula (2) above) and where I use the term normal operating conditions I mean conditions of steady flow through the carburetor which excludes momentary fluctuations due to sudden changes in throttleopening.

I obtain the foregoing results as follows. I first determine the fuel flow for each degree of pressure (vacuum) in the mixing chamber from formula (1) above. I then multiply these values by the proper multiple to give the desired mixture ratio. Thus, if a mixture ratio of 16 parts of air,

by weight, to 1 part of liquid fuel, is desired, I

multiplythe fuel flows, for each value of mixing chamber pressure, by 16 and thus arrive at the required air flow. I then determine the actual air flow, for each corresponding degree of pressure in the mixing chamber, from formula (2) above. As air, being an elastic fluid, expands and becomes less dense as the effective head increases, while liquid fuel, being an inelastic fluid maintains its density, the air flow, determined as above, is found to increase'at a relatively slower rate, compared to the liquid fuel, as the pressure (vacuum) in the mixing chamber increases.

This deficiency in the air flow is determined, for,

each degree of pressure in the mixing chamber .(Pm), by subtracting the value of G2, calculated fromformula (2) above for the corresponding value of Pm, from 16 G1, calculated from formula (1) above, for the same value of Pm. Conversely, the required pressure to be applied to the air supply to bring it up to a parity with the liquid fuel supply, for any degree of pressure in the mixing chamber, is determined by substituting the value of 16 G1, (computed as above) for G2 in formula (2) above, and solving for Pm. The resulting value of Pm, which we will denote as Pm, is the pressure required to supply the proper flow of air to the mixing chamber for the given pressure (vacuum) Pm, therein. Byway of illustration, let us suppose that when the pressure in the mixing chamber (Pm) is 10.7 pounds per square inch, (1. e. 4 pounds per square inch vacuum), the value of Fun, computed as above, is 5 pounds per square inch. In order then to maintain the required parity of flow (16:1) between the air and liquid fuel, it will be necessary to increase the pressure of the air flow at that point by 1 pound per square inch. This might be accomplished by subjecting the air supply to the mixing chamber to a superatmospheric pressure, equal to 1 pound per square inch, gauge, when the vacuum in the mixing chamber of the carburetor is 4 pounds per square inch, and which varies directly as the vacuum in the mixing chamber by an amount, determined as above, for each degree of vacuum in the mixing chamber.

From what has just been said, it follows that instead of subjecting the entire air supply to the mixing chamber to a superatmospheric pressure, in order to make it -maintain a parity with the liquid fuel flow, as indicated above, I may permit the main air supply to enter the mixing chamber under the influence of the vacuum therein alone,

i. e., the main air supply may be drawn into the mixing chamber, at atmospheric pressure by the vacuum in the mixing chamber, and the deficiency in the air supply thus incurred, may be furnished under superatmospheric pressure. In this case, the amount of superatmospheric (compressed) air is determined for each degree of pressure (vacuum) in the mixing chamber by 5 value of 16 G1G2, it follows that there is a direct relation between Pm and Pm, and hence, if the value of Pm can be controlled and made a function of Pm, then the correctamount of additional compressed air will automatically be fed into the mixing chamber for each corresponding value of the pressure (vacuum) (Pm) in said chamber. This is the essence of the invention in this case, and since the amount of compressed air furnished is exactly that required to bring the air flow up to a parity (16: 1) with the liquid flow forany pressure (vacuum) in the mixing chamber, it is apparent that the total air supply to the mixing chamber, for any degree of pressure (vacuum) therein, is in accordance with the law of liquid flow, i. e., the water formula (1) shown above, and not in accordance with the adiabatic formula (2) above, which normally governs the flow of air.

An object of this'invention is to provide a carburetor in which the liquid fuel is broken up within the fuel nozzle by compressed air so that it issues from said nozzle in a high state of atomization. 40 I Another'object of this invention is to provide a carburetor wherein a parity between the liquid fuel and air components of the fuel-air mixture is maintained by properly varying the pressure upon a part of the air supply so that the total air supply follows the law of liquid flow.

Still another object of this invention is to provide a carburetor in which only a small portion of the air supply is fed into the mixing chamber under pressure, but this portion is sufficient to completely atomize the entire liquid fuel component of the mixture and also compensate the mixture for the deficiency of air which results from the difference between the laws of flow of liquid and gases. 55

Still another object of this invention is to provide a carburetor in which parity between the liquid fuel and air supplies is secured by making the air supply follow the law of liquid flow.

With these and other objects in view which may be incident to my improvements, my invention consists in the combination and arrangement of elements hereinafter described and illustrated in the accompanyi iig drawing in which:

Figure 1 is a side elevation of my improved carburetor, showing in diagrammatic outline the main supply tank, air pump and connections therebetween, and in vertical section, the pressure regulator;

Figure 2 is a central longitudinal section, on an enlarged scale of my improved carburetor.

This invention broadly comprehends a liquid fuel supply under constant (atmospheric) pressure, a main air supply also under atmospheric pressure and a supplementary air supply under 75 superatmospheric pressure; the flows of the liquid fuel and main air being induced solely by the vacuum in the mixing chamber of the carburetor while the flow of supplementary air is caused by an effective head which consists of the vacuum in the mixing chamber and a variable superatmospheric pressure. This superatmospheric pressure varies between such limits and according to such a law, as will at all times cause the total air supply to bear a desired ratio to the liquid fuel supply. Thus, the supplementary air flow is such, at all times, as to equal the natural difference that always exists between a fluid flowing according to the law of liquid flow and according to the law of adiabatic gas flow. Since this supplementary air flow is under a. superatmospheric pressure it is also utilized to atomize the liquid fuel by feeding it into the mixing chamber through an atomizing nozzle.

Referring to Figure 2 of the drawing, theref- 4 erence numeral I, denotes the body of a carburetor having a. main air inlet 2, Venturi throat 3, mixing chamber 4, and mixture outlet 5 controlled by a butterfly throttlevalve 5 in the usual manner. Integral with the bottom wall of air inlet 2 and extending to a point just above the center of the Venturi throat 3, is an atomizing nozzle I consisting of an outer liquid fuel tube 3 and an inner air tube 9, the former surmounted by a cap I0, having a perforation I I, through which the fuel from the nozzle is discharged into the mixing chamber 4.

Fuel tube 3 communicates through a passageway and port I 3 with a liquid fuel reservoir I4 which is supplied by liquid fuel through an inlet IS controlled by a valve I6 which is actuated by a float II, so that the liquid fuel is always maintained in reservoir I4 at a constant level X-X. Float H has such a buoyancy as to always close valve I5 against the pressure of the liquid fuel in inlet I5 whenever the liquid level in reservoir I4 reaches the line X-X. Port I3 is controlled by a manually adjustable needle valve I 8 so as to regulate the flow of liquid fuel to nozzle I.

Reservoir I4 is closed by a cover I 9 which seats on a gasket 20 and is held in place by screws 2I.

Cover I9 has a vent hole 22 which enables atmospheric pressure to be exerted at all times on the liquid fuel in reservoir I4.

Air tube 9 communicates through a passageway J 23 whose width is greater than its depth, and pipe 24 with an air pump 25 which is geared to the engine (not shown). See Figure 1. Pump 25 is also connected by a pipe 26 to a main fuel supply tank 2I through a spring pressed check valve 23 and series of baiiies so arranged as to prevent liquid fuel splashing into pipe 26, and running into pump 25 when the automobile is going down hill. A pipe 29 conveys liquid fuel to the carburetor reservoir I4 under the superatmospheric pressure maintained in tank 21 by pump 25.

Pump 25 is of the conventional rotary impeller type having a plurality anda common air intake 3I provided with a check valve 32. g

In order to control the pressure in pipe 24, I have provided a novel form of pressure regulator 5| which consists of a cylindrical casing 52 divided into an upper chamber 33 and a lower chamber 34 by a partition 35, the upper chamberfl' being connected to pipe 24 by a pipe 33 and the lower chamber being connected to the pump 25 on its intake side by a pipe 31, as clearly shown in Figure l.

- uum in the mixing chamber governs the flow of of associated blades 30,

Partition 35 has a central tapered aperture 33 which serves as a seat for a tapered valve 39 passing through aperture 38'and fixedly attached to a piston 40. which is adapted to reciprocate in chamber 34 with an air-tight fit. Interposed 5 between the bottom of piston 40 and 'the bottom wall of easing 3| is a helical spring H which tends to push piston 40 upwardly in chamber 34 until the top of valve 39 contacts with the top wall of casing 3|, in which position the opening through aperture 38 is a maximum.

Piston 40 is made responsive to the vacuum in mixing chamber 4 by a pipe 42 which connects the mixing chamber 4 with chamber 34 below piston 40. From the foregoing description, it is clear that the position of piston 39 and therefore the degree of opening of aperture" 39 is dependent at all times upon the degree of vacuum in the mixing chamber 4, since when this vacuum is low, spring 4| pushes piston 40 up and when this vacuum is high it overcomes spring M and retracts piston 40.

Since the opening in aperture 38 governs the amount of air that is shunted around pump and this determines the pressure. in pipe 24, it follows that the pressure in pipe 24, and therefore in nozzle "I, is regulated by the valve 39 which in turn is subject to the vacuum in the mixing chamber 3. At the same time the vacair thereinto and, subject to the influence of the superatmospheric pressure in nozzle I, also the flow of liquid fuel. If the compressed air flow through pipe 24, passage 23 and tube 9 be disregarded, then the flows of air and liquid into the mixing chamber would be simply those due to the common vacuum existing in the mixing chamber at any time. But, as stated above, I

' have shown that where the air flow and liquid fuel flow are induced by a common vacuum, as this vacuum is increased, the liquid fuel flows faster than the air with a progressively increasing difference. If now a supplementary flow of air be supplied to the mixing chamber just suflicient to maintain the desired parity between the liquid 45 fuel and air supplies under varying operating conditions, the tendency of the mixture to overenrich at high speeds is compensated for and an optimum mixture is ,obtained. This result I accomplish by making the supplementa y air flow through the nozzle 1 just sufiicient a all times to compensate for the natural deficiency in the main air flow under all operating conditions. This is effected as follows. The minimum pressure on the air line 24 is made such as will effectively atomize the smallest flow of liquid fuel from the nozzle I when the engine is idling and the throttle is in the most restricted position (as shown in Figure 2) and no more. This pressure is very slight for such small liquid fuel 00 flows.

The pressure in line 24 is then progressively raised as the vacuum in the mixing chamber is increased,,but at a slightly greater rate of increase, as is required'for complete compensation. The rate of increase of pressure in line 24 is determined by the contour of valve stem 39. Thus, it will be noted that this stem is not truly conical, which would make the variation in pressure in line 24 in linear proportion tion in vacuum inthe mixing chamber, but has a convex contour which closes aperture 38 with a progressively increasing speed as stem 39 is moved downwardly by the vacuum in the mixing chamber 4. This results in building up the pres- 75 to the varia- I escaping from nozzle 1 which operates to somewhat increase the flow of liquid fuel from the i nozzle. As these two effects tend to neutralize each other,'their, net influence is small.

From the foregoing description, it is apparent that the main air supply entering air intake 2 and passing through Venturi throat 3 is utilized to meter the flow of liquid fuel, with due calibration for the qualifying effects of the compressed air escaping from nozzle 1 and that compensa-- tion of the mixture is secured by making the compressed air supply just sufficient for this purpose under all operating conditions. This compressed air supply is also utilized'to 'atomize the liquid fuel issuing from nozzle 1.

Many advantages flow from this novel arrangement. First, the extremely simple construction involved. The flow of supplementarv (compressed) air is governed by a metering restriction 43 placed in pipe 24 at its junction with carburetor body I, and the contour of valve stem 39 which regulates the pressure in line 24. These are factory adjustments. The only operating adjustments are the needle valve l8 which determines the strength of the mixture and the cap lflwhich determines the fineness of the atomization of the liquid fuel.

Second, the complete atomization of the liquid fuel due to the action of the compressed air.

Third, complete and accurate compensation of the mixture under all operating conditions, so that any desired fuel-air ratio may be obtained. Thus, if a slightly rich mixture is desired for idling and for high speed operation, and a lean mixture for economy at intermediate speeds, these results can be readily secured by the proper calibration of metering restriction 43 and valve stem 39.

Fourth, no special acceleration device is required since the sudden increase in vacuum in the mixing chamber 4, resulting from a quick opening of the throttle, immediately closes aperinto the mixing chamber under a superatmospheric pressure and this is immediately available to supply the increase of fuel required for quick acceleration. As soon as the vacuum in mixing chamber 4 stabilizes after the throttle is kicked open, the law of liquid fuel and air immediately stabilizes also, and uniform operating conditions are resumed.

The operation of my device is as follows: When the engine is started, pump 25 which .is geared thereto with a high gear ratio, at once delivers a jet of air to the mixing chamber through nozzle 1. This jet of air carries with it a relatively large amount of fuel whichis ejected from the nozzle by the aspirating effect of the escaping air. This rich mixture facilitates starting and makes unnecessary any special starting device, though, of course, a conventional choke may be used in the. air intake, if desired, to increase the suction on the nozzle I.

As the pump 25 is geared to the engine, it auto- 5 matically varies in speed with the engine and thus automatically varies the volume of compressed air supplied with the speed of the engine subject of course to the regulating effect of the pressure regulator.

The tension on check valve 28 is such that this valve is held closed until the speed of the pump is sufficient to build up the normal pressure in line 26 and open it. This insures that all of the compressed air produced by the pump upon starting 15 of the engine is delivered to the carburetor to insure quick and easy starting. Pressure is not necessary in the tank instantly upon starting as the fuel in the carburetor reservoir I4 is suflicient to run the engine until the pump 25 builds up its normal pressure. For this reason, the loss of pressure due to refilling tank 21 is of no consequence, as the reduced air space left when the tank is filled is quickly brought up to pressure by the pump before the fuel in reservoir I4 is exhausted.

While I have shown and described the preferred embodiment of my invention, I desire it to be understood that I do not limit myself to the constructional details shown by way of illustration as these may' be changed in combination and arrangement without departing from the spirit of my invention or exceeding the scope of the appended claims.

I claim: I

1. In a carburetor, a mixing chamber, and means for supplying air thereto at a rate which varies in accordance with the law of liquid flow, by supplying a portion of said air supply subject to a variable pressure.

2. In a carburetor, a mixing chamber, a main air supply thereto under atmospheric pressure, a supplementary air supply thereto under a superatmospheric pressure, and means to vary the pressure on the supplementary air supply so that the total air supply will be fed into said chamber according to the law of liquid flow.

3. In a. carburetor, a mixing chamber, means for supplying liquid fuel thereto under atmospheric pressure, and means for supplying air thereto at a rate which varies in accordance with the law of liquid flow, a portion of said air supply being subject to a variable pressure.

4. In a carburetor, a mixing chamber, means for supplying liquid fuel thereto under atmospheric pressure, a. main air supply and a supplementary air supply thereto, said supplementary air supply being subject to such a variable superatmospheric pressure as will cause the total air supply to be fed into said chamber in accordance with the law of liquid flow.

5. In a carburetor, a mixing chamber, means for supplying liquid fuel thereto under atmospheric pressure, a main air supply fed into said chamber in accordance with the law of adiabatic 5 gas flow, a supplementary air supply fed into said chamber at such a variable rate as equals the 8. In a carburetor, a mixing chamber, an at omizing nozzle therein, and means for supplying air to said chamber at a rate which varies in accordance with the law of liquid flow, a. portion of said air supply being fed into said chamber through said nozzle under a variable superatmospheric pressure.

9. In a carburetor, a mixing chamber, an atomizing nozzle therein, a main air supply to said chamber, and a supplementary air supply through said nozzle to said chamber, said supplementary supply being subject to a superatmospheric pressure varying inversely with the pressure in the mixing chamber, so that the total air supply is fed into said chamber in accordance with the law of liquid flow.

10. In a carburetor, a, mixing chamber, and means for supplying air thereto including vacuum-controlled means for subjecting a portion of said air supply to such a variable superatmospheric pressure as will cause the total of said air supply to be fed into said mixing chamber in accordance with the law of liquid flow.

11. In a carburetor, a mixing chamber, a main air supply thereto under atmospheric pressure, a supplementary air supply thereto under a superatmospheric pressure, and vacuum-controlled means to vary the pressure on the supplementary air supply so that the total airsupply will be fed into said chamber according to the law of liquid flow.

, 12. In a carburetor, a mixing chamber, means for supplying liquid fuel thereto under atmospheric pressure, and means for supplying air thereto, including vacuum-controlled means for subjecting a portion of said air supply to such a variable superatmospheric pressure as will cause the total air supply to be fed into said chamber at a rate which bears a desired predetermined ratio to the rate of said liquid fuel supply.

13. In a carburetor, a mixing chamber, an atomizing nozzle therein, and means for supplying air to said chamber, includrng vacuum-controlled means for feeding a portion of said air supply through said nozzle to said chamber under such a variable superatmnspheric pressure as will cause the total of said air supply to be fed into said chamber in accordance with the law of liquid flow.

14. ha carburetor, a mixingchamber, an air supply and a liquid fuel supply thereto, and means for regulating the pressure on a'portion of said air supply so that the total air supply enters said chamber at rate which bears a predetermined ratio to said liquid fuel supply under all normal operating conditions.

-15. In a carburetor, a mixing chamber, an air supply and a liquid fuel supply thereto, means for compressing a portion of said air supply, and

means for regulating the pressureon said portion of the air supply so that the total air supply enters said chamber at a rate which bears a predetermined ratio to said liquid fuel supply under all normal operating conditions.

16. In. a carburetor, a mixing chamber, an air supply and a liquidfuel supply thereto, and vacuum-controlled means for regulating the pressure on a portion of said 'air supply so that the total air supply enters said chamber at rate which bears a'predetermined ratio to said'liquid fuel supply under all normal operating conditions.

17. In a carburetor, amixing chamber, an air 10 supply and a liquid fuel supply thereto, and means, responsive to the pressure in said chamber, for regulating the pressure on a portion of said air supply so that the total air supply enters said chamber at rate which bears a predeter- 15 mined ratio to said liquid fuel supply under all f normal operating conditions.

18. In a carburetor, a mixing chamber, a main air supply, a supplementary air supply, and a liquid fuel supply thereto, and means for regu- 20 lating the pressure on said supplementary air supply so as to make the total air supplied to said chamber bear a predetermined ratio to said liquid fuel supply under all normal operating conditions. g5 19. In a carburetor, a mixing chamber, a main air supply, a supplementary air supply, and a liquid fuel supply thereto, and vacuum controlled means for regulating the pressure on said supplementary air supply so air supplied to said chamber bear a predetermined ratio to said liquid fuel supply under all normal operating conditions.

20. In a carburetor, a mixing chamber, a main air supply fed into said chamber in accordance 35 with the normal law of air flow, a supplementary air supply, and vacuum-controlled means to regulate the pressure on supply .so that the total air supplied to said chamber varies with respect to the pressure 40 therein in accordance with the law of liquid flow.

21. In a carburetor, a mixing chamber, means for supplying liquid fuel thereto under atmospheric pressure, and means for supplying air thereto including means for subjecting a portion 45 of said air supply to such a variable superatmospheric pressure as will cause the total of said air supply to be fed into said mixing chamber in accordance with the law of liquid flow.

22. In a carburetor, a mixing chamber, an atomizing nozzle therein, a main air supply to said chamber, and a supplementary air supply through said nozzle to said chamber, said supplementary supply being subject to such a variable superatmospheric pressure as will cause the 55 total air supply to be fed into said chamber in accordance with the law of liquid flow.

23. IITQ. carburetor, a mixing chamber, an air supply and a liquid fuel supply thereto, and means for regulating the pressure on a portion of 60 said air supply so that the total air supply enters said chamber at rate which bears a constant ratio to said liquid fuel supply under all normal operating conditions. I

24. In a carburetor, a mixing chamber, a main 65 air supply, a supplementary air supply, and a liquid fuel supply thereto, and means controlled by the pressure in said chamber, for regulating the pressure on said supplementary air supply so as to make the total air supplied to said chamber bear a predetermined ratio to said liquid fuel supply under all normal operating conditions.

25. In a carburetor, a mixing chamber, a main air supply fed into said chamber in accordance 7 as to make the total 30' said supplementary air" I with respect to the pressure therein in accordance with the law of liquid flow.

27. In a carburetor, a mixing chamber, a main air supply fed into said chamber in accordance with the normal law of air flow, a supplementary air supply, and means controlled by the pressure in said chamber, to regulate the pressure on said supplementary air supply so that the total air supplied to said chamber varies with respect to the pressure therein in accordance with the law 1 of liquid flow.

AUGUSTIN M. PRENTISS. 

